Subretinal Mononuclear Cells in Coats' Disease Studied with RPE65 and CD163: Evidence for Histiocytoid Pigment Epithelial Cells.

Purpose: To evaluate the mononuclear cells in the subretinal exudate in Coats' disease.

Design: Retrospective case series.

Methods: Five enucleated globes and 1 cytology sample from a patient with Coats' disease and 1 case of chronic retinal detachment following repair of an open globe injury were examined immunohistochemically to identify intraretinal and subretinal exudative cells. The 2 biomarkers were RPE65 for retinal pigment epithelium and CD163 for histiocytes, each tagged with different chromogens, yellow for pigment epithelium and purple for CD163-positive (CD163) monocytes/histiocytes. Expression levels were sought from both biomarkers together and singly. A color shift to red in the cells' chromogenic reaction indicated the simultaneous presence of the 2 biomarkers.

Results: Most of the mononuclear cells in Coats' disease samples were CD163 (purple), and a minority were RPE65 (yellow). An intermediate number of cells were RPE65/CD163 (orange-red). The eye with a chronic retinal detachment had an equal distribution of CD163 and RPE65/CD163 cells.

Conclusions: RPE has several well-delineated phenotypes and functions. In normal visual physiology, the pigment epithelium supports photoreceptors and participates in their renewal by phagocytosis of the tips of the photoreceptors. The expression of CD163, a feature of hematopoietically derived monocytes, together with RPE65 in the retinal pigment epithelium, supports differentiation toward histiocytes. Yellow staining of detached pigment epithelial cells were rare. The presence of histiocytoid pigment epithelium at the Bruch membrane probably also has implications for macular degeneration.